Liverpool have begun their latest title challenge in formidable and, often near flawless, fashion but Premier League win number seven came riddled with imperfections, reminding everyone that Jürgen Klopp’s side are mortal after all.A week after winning at Everton Chris Wilder’s Sheffield United more than matched their gilded visitors and seemed set to take at least one point before a ghastly, freakish, goalkeeping error on the part of the previously underemployed Dean Henderson handed Georginio Wijnaldum the winning goal. It was Liverpool’s first victory at Bramall Lane since 1990 and they are unlikely to forget it in a hurry.